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Conclusions and Recommendations
CONCLUSION: U.S. participation in Euclid would represent a valuable first step
toward meeting one of the science goals (furthering dark energy research) of
NWNH for WFIRST. However, Euclid on its own does not provide a viable
alternative for achieving the broader NWNH goals for the WFIRST mission, nor
does it achieve the more ambitious goals for WFIRST’s dark energy measurements.
Euclid will carry out an exciting science program that should yield important scientific results.
Benefits of U.S. participation in the Euclid Consortium should also include detailed knowledge of,
experience with, and access to Euclid instruments, data pipelines and products, simulations, and
modeling, and most importantly, opportunities for U.S. scientists to participate fully in this promising
mission. This knowledge could help optimize the science return of the WFIRST mission as well. Such an
investment will further the goals of NWNH, be helpful to the preparations for WFIRST, and enhance
WFIRST’s chances of success. The committee reached this conclusion that a U.S. role in Euclid would be
beneficial to U.S. science, although as NWNH concluded and as the committee heard in evidence
presented by several experts, Euclid cannot carry out the full science priorities envisioned in NWNH.
WFIRST will uniquely carry out the important NWNH goals of exoplanet studies and a guest
observer program.51 Moreover, the presentations to the committee that offered direct comparison of
Euclid and WFIRST capabilities for dark energy research showed clear advantages of WFIRST for both
the galaxy clustering (baryon acoustic oscillation, BAO) and weak gravitational lensing techniques that
make up the Euclid mission. In addition, WFIRST includes the supernova technique whose
demonstrated, well-characterized performance serves as an important complement to BAO and weak
gravitational lensing. When combined with the results of the Kepler mission, WFIRST’s gravitational
microlensing planet search will produce a comprehensive demographic survey running from Mercury-
scale orbits to beyond the snow line in hundreds of exo-solar systems, data that will provide an essential
observational constraint on the physics of planet formation. The remarkable potential of a deep multiband,
near-infrared galaxy survey over a large fraction of the sky and a stellar survey covering the galactic
plane and halo will go unrealized without WFIRST. These near-infrared surveys should deliver
significant science benefit to multiple areas of astronomy. WFIRST’s observations in Guest Observer
mode will, for example, invigorate studies of stellar evolution, providing precise ages for star clusters and
an infrared probe of the most vigorous sites of star formation in our Galaxy and its neighbors.
RECOMMENDATION: NASA should make a hardware contribution of
approximately $20 million to the Euclid mission to enable U.S. participation. This
investment should be made in the context of a strong U.S. commitment to move
forward with the full implementation of WFIRST in order to fully realize the
decadal science priorities of the NWNH report.
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RECOMMENDATION: In exchange for this small, but crucial, contribution, NASA
should secure through negotiation with the European Space Agency both a U.S.
position on the Euclid Science Team with full data access and the inclusion of a team
of U.S. scientists in the Euclid Consortium that would be selected by a peer-
reviewed process with full data access as well as authorship rights consistent with
Euclid policies still to be formulated.
As with all NASA missions, the expectation is that NASA will ensure and support access to the
Euclid data for the wider U.S. community once the proprietary data period has expired. This involvement
is especially important for Euclid, whose survey data should enable significant legacy science. Through
its direct involvement in Euclid, the U.S. science team will enhance not only the U.S. capabilities to study
dark energy but also the broader use of the Euclid data by the U.S. community. If software developed by
the U.S. Euclid team is made available to the community when the Euclid data become public, this step
also will enhance the broader community’s ability to use the Euclid data. While the U.S. role on the EST
should be more carefully delineated through negotiations with the European Space Agency, it could, for
example, involve leadership in Euclid legacy science, defined as providing value-added data products to
the community that combine relevant ground and space data sets (including those from WFIRST), given
the importance of data dissemination to the U.S. community.
NASA and the European Space Agency are discussing several possible options for the U.S.
hardware contribution. While the two agencies should determine the nature of the U.S. contribution,
contributions with the maximum science benefit to the Euclid mission will benefit both the European and
the U.S. communities.52 The reaction wheel could offer a significant improvement in mission efficiency.
The filter wheel would also provide some benefit to the mission and would take advantage of U.S.
expertise in designing filter wheels (e.g., for the Hubble Space Telescope). The near-infrared detectors, if
characterized by U.S. instrumentalists who have expertise in this area, would be beneficial but would
likely be the more expensive of the options.
The science goals of WFIRST go far beyond those of Euclid, and WFIRST is central to realizing
those goals and to maintaining U.S. leadership in astronomy and astrophysics in the next decade and
beyond. The committee notes that early expenditures on pre-phase A studies, particularly those that
engage the community, often accelerate mission timelines and reduce costs.
Mission collaboration costs often grow, as demonstrated by the U.S. participation in the Planck
mission discussed above. The committee recommends a tripwire for the hardware costs at 50 percent
above the recommended value of $20 million.
RECOMMENDATION: NASA should seek independent community review of any
financial commitment for hardware expenditures beyond $30 million for Euclid.
The committee recognizes that support for this science team will cost an additional ~$2 million
per year for about 10 years, for a total that is similar to the hardware investment. That is a necessary
expense and not the kind of increase discussed herein. Given the constraints on the NASA budget it is
crucial that the contribution to Euclid not grow and impact the rest of the space astrophysics program. The
Decadal Survey Implementation Advisory Committee (DSIAC) proposed and described in NWNH would
provide an appropriate mechanism for such a review.
CONCLUSION: The committee concludes that the combination of data from
planned U.S.-led ground-based surveys with Euclid and WFIRST data will enhance
the science return from both the ground- and space-based surveys, and that
a coordinated, strategic approach to managing these joint data sets could position
the U.S. community for a leadership role in their scientific exploitation.
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The necessity of ground-based data to Euclid’s scientific success provides a potential basis for
negotiating agreements between the ground-based projects and the Euclid mission, which could lead to
increased U.S. scientific participation in Euclid. The Department of Energy and the National Science
Foundation are the predominant sources of support for two of the U.S.-led ground-based projects, the
Dark Energy Survey and the Large Synoptic Survey Telescope. The degree to which these agreements
might be coordinated with the proposed NASA participation in Euclid is a matter that the Astronomy and
Astrophysics Advisory Committee, which is charged with considering interagency issues, could consider.
Obtaining the full scientific benefits of the combined ground- and space-based data will likely
require joint processing and analyses of the combined data sets at the pixel level. This deep level of
engagement in the data argues for direct collaboration between the ground- and space-based projects.
Such joint analyses would require significant data management resources that are not currently budgeted
within these projects.
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